Technical Field
The present disclosure relates to a lock-up device, and particularly to a lock-up device for a torque converter, which is configured to transmit a torque from a front cover to a transmission-side member through a turbine.
Background Information
Torque converters are often equipped with a lock-up device for directly transmitting a torque from a front cover to a turbine. Such a lock-up device includes a piston, an input-side plate, a plurality of torsion springs, and an output-side plate. The piston is capable of being coupled by friction to the front cover. The input-side plate is fixed to the piston. The torsion springs are supported by the input-side plate. The output-side plate is elastically coupled through the torsion springs to the piston and the input-side plate in a rotational direction. The output-side plate is fixed to the turbine.
Additionally, as described in Japan Laid-open Patent Application Publication No. 2012-237441, there has been also proposed a so-called multi-plate lock-up device that a plurality of clutch plates are used to increase its clutch capacity.
In the lock-up device described in Japan Laid-open Patent Application Publication No. 2012-237441, a clutch portion is disposed between the front cover and the turbine. The clutch portion includes a plurality of clutch plates. A lock-up state (power transmission state) is herein made when these clutch plates are pressed in contact with each other by the piston. In this state, a torque from the front cover is transmitted through the clutch portion directly to the turbine without intervention of a torque converter body.
In the lock-up device described in Japan Laid-open Patent Application Publication No. 2012-237441, the piston is configured to be activated by the hydraulic pressure and press the clutch plates, whereby the clutch plates are pressed in contact with each other. At this time, if the piston rapidly presses the clutch plates with a great force, shock occurs when the clutch-on state is made. It can be assumed to alleviate the shock by controlling the hydraulic pressure of hydraulic oil acting on the piston. However, it is not easy to control the hydraulic pressure so as not to cause the shock.